The present invention relates generally to asphalt coated fibrous mats and more particularly to an asphalt coated mat which in one embodiment is especially suitable as a roofing membrane, for example as a roofing underlayment, and which in a second embodiment is especially suitable as a facing material for foamed resin sheet material.
For many years, the roofing industry has utilized asphalt saturated ragfelt or other such organic fibrous mat as a water impervious membrane, for example as a shingle underlayment or as part of a built-up roof. More recently, a number of companies in the roofing industry have turned their attention to glass fiber material as a substitute for ragfelt in this particular area. However, whether the roofing membrane has an organic base or an inorganic base, there are a number of required physical characteristics which it must exhibit, of course depending upon its ultimate intended use. For example, the membrane must meet minimum strength requirements, again depending upon its ultimate intended use, it must have a certain degree of resistance to the elements, for example to extremely low temperatures and extremely high temperatures, and it must be a product which can be readily handled and applied in the field. Moreover, the membrane must be one which reliably performs its main function which of course is to act as a barrier to liquids, specifically water. It is primarily this latter characteristic, i.e., the water impermeability of the membrane, that Applicant finds the prior art membranes lacking and to which the present invention is directed, as will become apparent hereinafter.
The main reason that many presently available asphalt roofing membranes are not completely satisfactory as water barriers resides primarily in the selection of the asphalt coatings. More particularly, most if not all of the asphalt mixtures are applied hot, that is, the asphalt in the mixture is heated to its melting point before being applied to the base sheet. The particular type of asphalt selected will depend on the nature of the base sheet itself. For example, where the base sheet is organic, for example ragfelt, the asphalt will generally be a saturant asphalt, i.e., one having a melting point of about 115.degree. F.-150.degree. F. and where the base sheet is inorganic, specifically glass mat, the asphalt selected will generally be a coating asphalt having a melting point of about 200.degree. F.-240.degree. F. In either case, Applicant has found that when a reasonable amount of the asphalt or what should be a reasonable amount is applied to the base sheet by means of the typical "hot melt" procedure, the ultimate article is far from pinhole free. Applicant has found this to be true even where a large amount of asphalt is used to saturate or coat the base sheet. The exact reason why pinholes occur is not exactly clear. However, the fact that they do occur reduces substantially the water impermeability of the membrane.
Another drawback resulting from this hot melt procedure is that the end product, specifically the asphalt in the end product, tends to be extremely tacky when subjected to high ambient temperatures. This is of particular concern where the membrane is packaged and shipped in rolls. If a separating medium is not used, the material if subjected to high ambient temperatures will tend to stick to itself in the roll. To prevent this from occurring, as the membrane is produced and rolled, a separating medium, for example sand or talc, is applied between its various layers. While this separating medium functions in the manner intended, it does add cost to the end product and also weight. Moreover, it tends to be a nuisance to the roofer.
As will be seen hereinafter, by selecting a particular asphalt mixture, specifically one meeting certain criteria, Applicant has substantially reduced if not completely eliminated the pinholes from his ultimately formed membrane. Moreover, this membrane does not tend to become tacky when exposed to high ambient temperatures and hence can be packaged in rolls without utilizing talc, sand or other such separating mediums.